Reversible-Deactivation Radical Polymerization in the Presence of Metallic Copper. Activation of Alkyl Halides by Cu0

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• 作者：Chi-How Peng ; Mingjiang Zhong ; Yu Wang ; Yungwan Kwak ; Yaozhong Zhang ; Weipu Zhu ; Matthew Tonge ; Johannes Buback ; Sangwoo Park ; Pawel Krys ; Dominik Konkolewicz ; Armando Gennaro ; Krzysztof Matyjaszewski
• 刊名：Macromolecules
• 出版年：2013
• 出版时间：May 28, 2013
• 年：2013
• 卷：46
• 期：10
• 页码：3803-3815
• 全文大小：528K
• 年卷期：v.46,no.10(May 28, 2013)
• ISSN：1520-5835

文摘

The rate coefficients for activation (k_a0^app) of two alkyl halides, methyl 2-bromopropionate, MBrP, and Br-capped poly(methyl acrylate), by Cu⁰ were determined under various conditions. The value of k_a0^app was studied in two solvents, dimethyl sulfoxide (DMSO) and acetonitrile (MeCN), and their mixtures with methyl acrylate (MA), using tris[2-(dimethylamino)ethyl]amine (Me₆TREN) and tris(2-pyridylmethyl)amine (TPMA) as ligands. The experiments showed that the rate of activation increased with the surface area of Cu⁰ but was typically not affected by the ratio of ligand to initiator, if a sufficient amount of ligand was present. The choice of solvent and presence of monomer/polymer had a small influence on k_a0^app. The activation rate coefficient of MBrP was k_a0^app= 1.8 脳 10^鈥? cm s^鈥? with Me₆TREN as the ligand in DMSO at 25 掳C while the activation rate coefficient of Br-capped poly(methyl acrylate) by Cu⁰ was slightly lower, k_a0^app = 1.0 脳 10^鈥? cm s^鈥?, as measured in a polymerization of MA in MA/DMSO = 1/1 (v/v) with Me₆TREN. On the basis of the measured rate coefficients, the activation rate of MBrP by 1 mM Cu^IBr/Me₆TREN (k_a1^app = 3.2 脳 10² M^鈥? s^鈥?) is similar to the activation rate by 2 km Cu⁰ wire with diameter of 0.25 mm in 7 mL of DMSO. Thus, under typical conditions, conducted in the presence of ca. 1 cm Cu⁰ wire, alkyl halides are predominantly activated by Cu^I species. Consequently, Cu⁰ acts as a supplemental activator and also as a reducing agent (SARA) because comproportionation dominates disproportionation, for the polymerization of MA in DMSO. These results support the SARA ATRP mechanism rather than the proposed single electron transfer鈥搇iving radical polymerization (SET-LRP) process, which requires exclusive activation by Cu⁰ and instantaneous disproportionation of Cu^I.